80 lines
1.5 KiB
Go
80 lines
1.5 KiB
Go
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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// See page 88.
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// Append illustrates the behavior of the built-in append function.
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package main
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import "fmt"
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func appendslice(x []int, y ...int) []int {
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var z []int
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zlen := len(x) + len(y)
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if zlen <= cap(x) {
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// There is room to expand the slice.
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z = x[:zlen]
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} else {
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// There is insufficient space.
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// Grow by doubling, for amortized linear complexity.
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zcap := zlen
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if zcap < 2*len(x) {
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zcap = 2 * len(x)
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}
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z = make([]int, zlen, zcap)
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copy(z, x)
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}
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copy(z[len(x):], y)
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return z
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}
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//!+append
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func appendInt(x []int, y int) []int {
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var z []int
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zlen := len(x) + 1
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if zlen <= cap(x) {
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// There is room to grow. Extend the slice.
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z = x[:zlen]
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} else {
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// There is insufficient space. Allocate a new array.
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// Grow by doubling, for amortized linear complexity.
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zcap := zlen
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if zcap < 2*len(x) {
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zcap = 2 * len(x)
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}
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z = make([]int, zlen, zcap)
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copy(z, x) // a built-in function; see text
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}
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z[len(x)] = y
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return z
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}
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//!-append
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//!+growth
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func main() {
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var x, y []int
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for i := 0; i < 10; i++ {
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y = appendInt(x, i)
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fmt.Printf("%d cap=%d\t%v\n", i, cap(y), y)
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x = y
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}
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}
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//!-growth
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/*
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//!+output
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0 cap=1 [0]
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1 cap=2 [0 1]
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2 cap=4 [0 1 2]
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3 cap=4 [0 1 2 3]
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4 cap=8 [0 1 2 3 4]
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5 cap=8 [0 1 2 3 4 5]
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6 cap=8 [0 1 2 3 4 5 6]
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7 cap=8 [0 1 2 3 4 5 6 7]
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8 cap=16 [0 1 2 3 4 5 6 7 8]
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9 cap=16 [0 1 2 3 4 5 6 7 8 9]
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//!-output
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*/
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